The audience for this exam includes individuals who are responsible for optimizing network performance and implementing quality of service (QoS) for converged networks. Experience with implementing QoS and Voice over IP (VoIP) networks will help you prepare for this exam.

Which statement correctly specifies the characteristics of TCP, UDP and RTP with respect to reliability, reordering and time-stamping?

A. UDP does not provide reliability and reordering, but it does provide time-stamping. B. RTP does not provide reliability, but it does provide reordering and time-stamping. C. TCP provides reliability, reordering and time-stamping. D. RTP provides reliability, reordering and time-stamping.

Answer:B

Tutorial:Realtime Transport Protocol (RTP) provides sequence numbering (reordering) and time-stamping, but it does not offer reliability. The reliability feature of TCP is not suitable for voice applications. Therefore, RTP is used to transport digital voice in packet telephony networks.

User Datagram Protocol (UDP) provides no reliability, no sequence numbering (reordering) and no time-stamping. Lack of the latter two features makes UDP unsuitable for transporting voice.

TCP provides reliability and sequence numbering but not time-stamping. Time-stamping is a feature required for transporting voice. The acknowledgement and segment resending features of TCP make it a reliable transport protocol but too slow for voice transport. Also, the reliability feature of retransmitting lost data is not useful for voice applications.

Which statements apply to the policy-map command? (Choose all that apply.)

A. It specifies where the policy will be implemented. B. It specifies what will be done to the traffic. C. It contains a case-sensitive name and one or more traffic classes, each of which may have a QoS policy applied to it. D. It contains three main elements: a case-sensitive name, one or more match statements and an instruction on how to evaluate multiple match statements. E. It specifies what traffic you care about.

Answer:B, C

Tutorial:A policy-map command contains a case-sensitive name and one or more traffic classes, each of which may have a QoS policy applied to it. Up to 256 traffic classes can be associated with a single-traffic policy. Multiple policy-maps can be nested to influence the sequence of QoS actions. A policy-map defines what will be done to the traffic.

The service-policy command specifies where a policy (policy-map) is applied.

Each traffic class is defined using a class-map. A class-map command contains three main elements: a case-sensitive name, one or more match statements and an instruction on how to evaluate multiple match statements. A class-map can be configured in one of two modes: match all, meaning all conditions must be satisfied and match any, meaning that one condition satisfied is enough. Match all is the default mode for class-maps. The class-map command defines what traffic you care about.

Tutorial:The priority field on the ISL and 802.1Q/P frames is referred as the class of service (CoS) field. CoS is one of the main link layer markers (marking fields). Other examples of link layer markers are DE on Frame Relay and EXP on Multiprotocol Label Switching (MPLS).

The least important two bits in the Type of Service (ToS) byte in an IP packet are the Explicit Congestion Notification (ECN) bits. The six most important bits of the ToS byte are the Differentiated Services Code Point (DSCP) bits. DSCP bits are marker bits used for QoS, but the ECN bits are used for flow-control purposes.

MPLS is the acronym for Multiprotocol Label Switching. On MPLS packets, the EXP field is used for marking.

The IEEE 802.1Q standard defines a 4-byte header that is added to the Ethernet frame header after the source MAC address field. 802.1Q is used as a trunking mechanism between Ethernet LAN devices. The priority or CoS field is used for marking in the 802.1Q header. References:Introducing Classification and Marking: Marking, Optimizing Converged Cisco Networks, Module 4

Tutorial:In the Split-MAC architecture, processing of 802.11 data and management protocols and access point capabilities are distributed between a lightweight access-point (LWAP) and a centralized wireless LAN controller (WLC).

Time-sensitive and real-time functions, such as beacon generation, probe response and MAC layer encryption, are handled in the LWAP.

Non-real-time functions, such as 802.11 management protocol, frame translation and bridging functions, plus system-wide policies for user mobility, QoS and security, are handled by the WLC.